REACTION CONTROL

Evening Post, Volume CX, Issue 68, 17 September 1925, Page 14

REACTION CONTROL

A 'niethod of reaction control- •which has lately, come into fashion and , is highly praised by those who have tried it makes use of condenser placed I in? the plate circuli of the .'de-, teotor valve where' the "by-pass" 'condenser is usually placed; that is, across the telephone or fint transformer primary terminsJs, in conjunction with the usual,tickler.,or reaction' co.il.'":'lnVrthi' ordinary three-coil receiver reaction is much more effective when a by-pail condenser is used, because the radio-fre-quency current changes in* the tickler circuit are enabled to travel more/easilypast the high -.impedance; of tht> telephones or transformer; 'The smaller the condenser, the more these high-fre-quency current* are choked\back; If, therefore, a variable condenser is used, it can be operated as a control, with the tickler 'coiljplaced -in a more "or less fixed position.. The condenser, which need!not be of high quality, should have a total capacity of. .0005 or .001 mfd., and with the smaller, of these sizes it may be necessary to, use a .'-fixed one'of., the same size.in parallel with it, though this will depend on the size of the reaction coil used. control of reaction is convenient'with, circuits built behind thejpanel; the reaction coii can then be rigidly fixed. One advantage, of this/control is that; adjustment of the reaction has less effect on; the tuning of the secondary circuit than the movement of the reaction coil. ■; .'.■■'

■ Another simple form of reaction control which enables one to'use a, semifixed reaction coil is to shunt the coil , with a variable resistance, but the value of this may be rather critioal, and a variable resistance of the correct value may not, be .easily, available. : However, many experimenters have at hand some silch instrument as a dUcarded potentiometer. If so; it can: be used indirectly. One or two turns of wire may be wound'round the-tickler coil; with one end. connected ./to one , end of the potentiometer and the other end to the moving arm. This will provide a shortcircuited absorbing coil of variable tceistanoe, and will probably,•■:.be found quite a satisfactory reaction control. •At the same time it must be said that, if a three-coil tuner, is nicely,made, so that the reaction .coil can be delicately moved, and if one. has "good hands/ no fancy regeneration control is ■ really any better than that given by the moveable 'coil.,= :•■ .'■• „■';■ : :.;, .■•'. ;",;/- \\ '•' ;' ■'